Cost to Coast

[HondaHound]

Hi,

I just heard about Hypermiling yesterday. I had no idea! I thought I had no options in getting better MPG but now I see a few good techniques. My question is on the Pulse and Glide thang...

I have a 1997 Civic automatic transmission.
What is the difference (in gas savings) between P&G in neutral with the car being on & off? I ask because I'd rather not turn the car off while I'm driving. just because it's a pain. Does the car have to be turned off to get better gas mileage using P&G? Or will being in Neutral save gas?

thanks!

HHINLA

[roflwaffle]

Depending on what your speed and idle fuel consumption are coasting in neutral may save gas. If the engine is at a high enough load, it probably won't. It really depends on the situation. Determining how much load is on the engine during a portion of your trip is the best way to accurately figure out whether or not popping in/out of gear is worthwhile in terms of fuel savings.

[SVOboy]

^ he's smart.

Get some instrumentation and see for yourself, though, . It'll be worth it.

Welcome to EM!

[Gregte]

In my 4 cyl GMC if I coast in neutral with the engine running it is burning 1.2 ounces of gasoline per minute. With the engine off it is of course not burning any.

So it would take less than 2 hours of coasting in neutral, with engine running, to burn a gallon of fuel.

If I coast down hill, in gear, such that the engine is braking the vehicle, it burns no fuel. But if I coast down the same hill in neutral, using the brakes to slow the vehicle, it is again burning 1.2 ounces of gasoline per minute. So it is much better to have it in gear than in neutral while coasting down hill, if I need to slow the vehicle.

[Daox]

You'll really want to check your owners manual before doing any engine off coasting with an automatic transmission. If your manual says your car can be flat towed you are okay to engine off. If it says you can't flat tow, its likely you will damage your tranny over time due to lack of lubrication and pumps not running.

The benefit of engine off is definitly there. If you do a search its been asked a few times and there are some good answers out there. How big a difference really comes down to how much fuel your engine uses at idle. Larger engines will use more. Older and inefficient engines will use more. My Paseo's 1.5L (in current modified state) uses more fuel idling than my Matrix's stock 1.8L engine. Instrumentation is the only way to know this.

[HondaHound]

Originally Posted by SVOboy

^ he's smart.

Get some instrumentation and see for yourself, though, . It'll be worth it.

Welcome to EM!

Ok, sounds reasonable. What is the best instrumentation to get? Will ScanGuage tabulate the engine load? I'm not a super technical person but I'm willing to spend some time and money on this stuff. I read some great info on making the car more aerodynamic. I think I'll do that as well. Thanks for the comments!

HHINLA

[HondaHound]

Hi,

Just got my ScanGuage II and I've been messing around with it. I haven't tested Engine Load in Neutral while moving yet. But, I have done a little testing while at stop lights. It seems the Engine load is slightly greater when In D4 at a stop rather than put in Neutral. I get around 34 LOD in drive and around 30 LOD in neutral stopped. I'm wondering if that will make any difference with the MPG or if it's not even worth it.

I'll do some tests with LOD while in neutral while I'm coasting next week. Though I have an automatic which switches off the fuel injector while in coast anyway. If this is the case maybe it wouldn't make any difference?

HHINLA

[orange4boy]

Hondahound,

Something you might want to try is the engine load at idle with all accessories off then try it with blower fan, defrost, low beams highbeams, turnsignals, brake lights etc. This may give you an indication of alternator load and how that affects idle and driving fuel consumption. To check residual load you could unplug your alternator.

I'm curious and my van can't have a scanguage

I'm running on deep cycle batteries to eliminate these drains. I have not done the testing to see how much benefit I get but MetroMPG has Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

Good luck.

[PaleMelanesian]

Watch the gph gauge in D and in neutral. gallons per hour. In the automatics I've checked, neutral does indeed use less.

[HondaHound]

Originally Posted by PaleMelanesian

Watch the gph gauge in D and in neutral. gallons per hour. In the automatics I've checked, neutral does indeed use less.

Aha! Thanks for the tip! I'll report back.

HHINLA